1. Field of the Invention
This invention relates to a working apparatus for roughening the side of an optical fiber, particularly an optical fiber ribbon consisting of optical fibers arranged in the form of tape, to allow light to leak uniformly through the side.
2. Description of the Prior Art
Most of the prior art apparatus are provided, for illumination of the function display part in dark, with a illumination unit which consists of an acrylic resin light guide, a lamp, and a light emitter such as LED.
The illumination unit of this type however has a structural disadvantage that the lamp is necessary to be disposed on the back of the display, and this presents difficulties such as rise in display temperature and uneven illumination.
For this reason, illumination units free of the abovementioned defects have been developed. For example, illumination methods based on the construction that optical fiber ribbon have a section allowing light to leak on the side and this portion is disposed on the back of the display is disclosed in Japanese Laid-open Utility Models Nos. 9205/1987 and 9206/1987.
According to these methods, as shown in FIG. 3, an optical fiber ribbon 36 is interposed between a cushion 35, as on a plate, and an emery paper 33, and the latter is pressed against the side of the optical fiber ribbon by means of a hot stamper 31 with heating elements 32, so that the affected section (referred to as light-leakage section hereinafter) of the side becomes roughened to allow light to leak.
The thus-worked optical fiber ribbon has light leakage characteristics, particularly of the light leakage section, as represented by graph in FIGS. 2a and 2b, when a lamp is attached to either and each ends, respectively, of the optical fiber ribbon.
In these cases difficulty is encountered: FIG. 2a is the graph plotting the measured results of luminance passing through the light-leakage section 21 of the worked optical fiber ribbon 22 with a light source at one end and indicating a tendency of the luminance to fall with distance from the light source. On the other hand, the optical fiber ribbon similarly worked but with a light source at each end results in the graph (FIG. 2b) indicating the luminance to be high in the vicinity of each end of the ribbon and low in the neighborhood of the center. In FIG. 2b are designated optical fiber ribbon 4, light source 7, and light leakage section 8.